multi-touch demo: if an index 64 would come in, this would be written in the wrong...

multi-touch demo: if an index 64 would come in, this would be written in the wrong place in the cursor buffer. Supporting 64 IDs means writing to slots 0--63

(cherry picked from commit bef94a71b19e92de5ff82b620fbac853bf83a15b)

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@1806 7f0cb862-5218-0410-a997-914c9d46530a